In recent years, products using a liquid crystal panel such as a television receiver, a mobile phone, and a handheld terminal are increasing. Also, the demand of the large-sized thin flat panel is increasing. In a semiconductor integrated circuit for controlling the display of the liquid crystal panel, a high-speed operation is required to realize double speed drive to reduce a residual image in the display of an image and to allow smooth change of the image, in addition to realization of a 3D (3-dimensional) image.
A technique of an operational amplifier to improve a slew rate is disclosed in Patent Literature (JP 2006-094534A). The operational amplifier is provided with a first supply voltage rail section, a second supply voltage rail section, an input stage, a folded cascade connection stage, an output driver stage and a compensation circuit. The input stage includes a first input terminal and a second input terminal. The folded cascade connection stage is provided with first to fourth nodes and is connected to an output of the input stage. The output driver stage is provided with first and second output transistors which are respectively connected to the first and second nodes of the folded cascade stage, and outputs a drive current to an output node of the operational amplifier. The compensation circuit is provided with first and second capacitors, and first to fourth switches and is connected to the third and fourth nodes of the folded cascade connection stage and the output node of the operational amplifier. The output node is connected to the second input terminal of the input stage. The first switch and the first capacitor are connected in series between the first supply voltage rail section and the output node. The second switch and the second capacitor are connected in series between the second supply voltage rail section and the output node. The third switch is connected to the third node of the folded cascade connection stage between the first switch and the first capacitor. The fourth switch is connected to the fourth node of the folded cascade connection stage between the second switch and the second capacitor. Moreover, the compensation circuit is provided with the third capacitor between the third node of the folded cascade connection stage and the output node, and is provided with the fourth capacitor between the fourth node of the folded cascade connection stage and the output node.
In this way, the above-mentioned operational amplifier has phase compensation capacitors which are connected in parallel to improve a slew rate. In the section in which the output voltage changes, only the one of the phase compensation capacitors connected in parallel is used. Therefore, there is a fear that the amplification operation becomes instable.